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Auto merge of #122917 - saethlin:atomicptr-to-int, r=nikic

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Add the missing inttoptr when we ptrtoint in ptr atomics

Ralf noticed this here: https://github.com/rust-lang/rust/pull/122220#discussion_r1535172094

Our previous codegen forgot to add the cast back to integer type. The code compiles anyway, because of course all locals are in-memory to start with, so previous codegen would do the integer atomic, store the integer to a local, then load a pointer from that local. Which is definitely _not_ what we wanted: That's an integer-to-pointer transmute, so all pointers returned by these `AtomicPtr` methods didn't have provenance. Yikes.

Here's the IR for `AtomicPtr::fetch_byte_add` on 1.76: https://godbolt.org/z/8qTEjeraY
```llvm
define noundef ptr `@atomicptr_fetch_byte_add(ptr` noundef nonnull align 8 %a, i64 noundef %v) unnamed_addr #0 !dbg !7 {
start:
  %0 = alloca ptr, align 8, !dbg !12
  %val = inttoptr i64 %v to ptr, !dbg !12
  call void `@llvm.lifetime.start.p0(i64` 8, ptr %0), !dbg !28
  %1 = ptrtoint ptr %val to i64, !dbg !28
  %2 = atomicrmw add ptr %a, i64 %1 monotonic, align 8, !dbg !28
  store i64 %2, ptr %0, align 8, !dbg !28
  %self = load ptr, ptr %0, align 8, !dbg !28
  call void `@llvm.lifetime.end.p0(i64` 8, ptr %0), !dbg !28
  ret ptr %self, !dbg !33
}
```

r? `@RalfJung`
cc `@nikic`
This commit is contained in:
bors 2024-04-15 08:07:47 +00:00
commit 5dcb678ad8
2 changed files with 46 additions and 4 deletions
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12
compiler/rustc_codegen_llvm/src/builder.rs
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@ -1149,12 +1149,12 @@ impl<'a, 'll, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'll, 'tcx> {
order: rustc_codegen_ssa::common::AtomicOrdering,
) -> &'ll Value {
// The only RMW operation that LLVM supports on pointers is compare-exchange.
if self.val_ty(src) == self.type_ptr()
&& op != rustc_codegen_ssa::common::AtomicRmwBinOp::AtomicXchg
{
let requires_cast_to_int = self.val_ty(src) == self.type_ptr()
&& op != rustc_codegen_ssa::common::AtomicRmwBinOp::AtomicXchg;
if requires_cast_to_int {
src = self.ptrtoint(src, self.type_isize());
}
unsafe {
let mut res = unsafe {
llvm::LLVMBuildAtomicRMW(
self.llbuilder,
AtomicRmwBinOp::from_generic(op),
@ -1163,7 +1163,11 @@ impl<'a, 'll, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'll, 'tcx> {
AtomicOrdering::from_generic(order),
llvm::False, // SingleThreaded
)
};
if requires_cast_to_int {
res = self.inttoptr(res, self.type_ptr());
}
res
}
fn atomic_fence(